Query Processing (in Relational Databases)

Synonyms

Definition

Query processing denotes the compilation and execution of a query specification usually expressed in a declarative database query language such as the structured query language (SQL). Query processing consists of a compile-time phase and a runtime phase. At compile-time, the query compiler translates the query specification into an executable program. This translation process (often called query compilation) is comprised of lexical, syntactical, and semantical analysis of the query specification as well as a query optimization and code generation phase. The code generated usually consists of physical operators for a database machine. These operators implement data access, joins, selections, projections, grouping, and aggregation. At runtime, the database engine interprets and executes the program implementing the query specification to produce the query result.